Process For Manufacturing Spherical Activated Carbon

ABSTRACT

A process for manufacturing a spherical activated carbon, characterized by comprising the steps of: (1) forming a spherical substance of a heat-fusible resin, (2) oxidizing the spherical substance of a heat-fusible resin to form a heat-infusible spherical substance, and (3) activating the heat-infusible spherical substance to form the spherical activated carbon is disclosed. According to the process for the manufacture, a spherical activated carbon having desirable properties, such as an average particle diameter, a particle size distribution, a pore volume, or a specific surface area, can be easily prepared.

TECHNICAL FIELD

The present invention relates to a process for manufacturing a sphericalactivated carbon.

BACKGROUND ART

In patients suffering a lack of a renal function or a liver function,harmful toxic substances are accumulated or formed in bodies, such asblood, with a progress of a disorder of the organ functions, and thus anencephalopathia occurs, such as a disturbance of consciousness oruremia. Yearly, there is a growing number of such patients, andtherefore, the development of an organ-substitute apparatus ormedicament having a function to remove toxic substances from bodies, inplace of such defective organs, has become a serious problem. A methodfor removing toxic substances by hemodialysis as an artificial kidney isprevalent. Nevertheless, the hemodialysis-based artificial kidneyrequires a special apparatus, and thus, a skilled specialist is requiredfrom a safe operation standpoint. Further, blood must be taken from apatient's body, and thus, there are disadvantages in that patients mustbear high physical, mental and economic burdens. Accordingly,hemodialysis is not satisfactory.

As a means of remedying the above disadvantages, an oral adsorbent whichcan be orally administered and cure a disorder of renal and liverfunctions was developed and utilized [Patent Reference No. 1]. Theadsorbent disclosed in Patent Reference No. 1 comprises a porousspherical carbonaceous substance having particular functional groups,that is, a surface-modified spherical activated carbon, having. a highsafety factor and stable to a body, and having a useful selectiveadsorbability; that is, an excellent adsorbability of harmful substancesin the presence of a bile acid in an intestine, and a low adsorbabilityof useful substances such as digestive enzymes in the intestine. Forthese reasons, the oral adsorbent is widely and clinically used for apatient suffering from a disorder of a liver or renal function, as anadsorbent having few side effects such as constipation. The aboveadsorbent disclosed in Patent Reference No. 1 was prepared by forming aspherical activated carbon from a pitch such as a petroleum pitch as acarbon source, and then carrying out an oxidizing treatment and areducing treatment.

Further, an adsorbent for an oral administration providing animprovement in the above useful selective adsorbability, that is, anexcellent adsorbability of harmful substances and a low adsorbability ofuseful substances in the intestine, is known (Patent Reference No. 2).The adsorbent for an oral administration disclosed in Patent ReferenceNo. 2 is based on a finding that the above selective adsorbability isimproved within a special range of a pore volume, that is, when a volumeof pores having a pore diameter of 20 to 15000 nm is from not less than0.04 mL/g. to less than 0.10 mL/g. The adsorbent for an oraladministration is very effective in treating diseases where a sufficientadsorption of toxins and a reduced adsorption of useful substances inthe intestine are desired. The adsorbent disclosed in Patent ReferenceNo. 2 was also prepared by forming a spherical activated carbon from apitch such as a petroleum pitch as a carbon source, and then carryingout an oxidizing treatment and a reducing treatment.

[Patent Reference No. 1]

Japanese Examined Patent Publication (Kokoku) No. 62-11611

[Patent Reference No. 2]

Japanese Patent No. 3522708 (Japanese Unexamined Patent Publication(Kokai) No. 2002-308785)

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

In the surface-modified spherical activated carbon as mentioned above,it is expected that, if a pore volume, an average particle diameter, orthe like varies, adsorbing properties or selective adsorbability ofharmful substances are changed, and there is a possibility that asurface-modified spherical activated carbon having unknown excellentproperties is developed.

In the prior art, the surface-modified spherical activated carbon asmentioned above was produced by preparing a spherical activated carbonfrom a pitch such as a petroleum pitch as a carbon source, and thencarrying out an oxidizing treatment and a reducing treatment. In casethat a spherical activated carbon is produced from a pitch as a carbonsource, however, it is not necessarily easy even in the laboratory tocontrol the properties, such as a pore volume, an average particlediameter, or the like, and it is very difficult to establish a processfor large-scale production.

Accordingly, the problems of the present invention are to provide ameans for facilitating a control in obtaining desired properties, suchas a pore volume, an average particle diameter, or the like, when aspherical activated carbon as a raw material of the surface-modifiedspherical activated carbon as mentioned above is prepared.

Means for Solving the Problems

The above problems can be solved according to the present invention, bythe process for manufacturing a spherical activated carbon,characterized by comprising the steps of:

-   (1) forming a spherical substance of a heat-fusible resin,-   (2) oxidizing the spherical substance of a heat-fusible resin to    form a heat-infusible spherical substance, and-   (3) activating the heat-infusible spherical substance to form the    spherical activated carbon.

In a preferable embodiment of the present process, the sphericalactivated carbon wherein an average particle diameter is 0.01 to 1 mm, aspecific surface area determined by a BET method is 700 m²/g or more,and a volume of pores having a diameter of 7.5 to 15000 nm is 0.01 mL/gto 1 mL/g is obtained.

A preferable embodiment of the present process further comprises thestep of:

-   oxidizing and reducing the spherical activated carbon to form a    surface-modified spherical activated carbon.

In a preferable embodiment of the present process, the surface-modifiedspherical activated carbon wherein an average particle diameter is 0.01to 1 mm, a specific surface area determined by a BET method is 700 m²/gor more, a volume of pores having a diameter of 7.5 to 15000 nm is 0.01mL/g to 1 mL/g, a total amount of acidic groups is 0.30 to 1.20 meq/g,and a total amount of basic groups is 0.20 to 0.90 meq/g is obtained.

In a preferable embodiment of the present process, the heat-fusibleresin is cross-linked vinyl resin.

In a preferable embodiment of the present process, a specific surfacearea of the spherical substance of a heat-fusible resin is 10 m²/g ormore.

In a preferable embodiment of the present process, a content of elementsother than a carbon atom, a hydrogen atom, and an oxygen atom in theheat-fusible resin is 15% by weight or less.

In a preferable embodiment of the present process, the sphericalactivated carbon or the surface-modified spherical activated carbon foran adsorbent for an oral administration is prepared.

Effects of the Invention

According to the manufacturing process of the present invention, variousproperties, such as a pore volume or an average particle diameter, ofthe produced spherical activated carbon can be easily controlled bychanging various manufacturing conditions in the manufacturing process.Therefore, a surface-modified spherical activated carbon having desiredvarious properties, such as a pore volume or an average particlediameter, can be easily obtained by further oxidizing and reducing theresulting spherical activated carbon.

BEST MODE FOR CARRYING OUT THE INVENTION

The first step in the manufacturing process of the present invention isto form a spherical substance of a heat-fusible resin, that is, aheat-fusible resin sphere.

The term “heat-fusible resin” as used herein means a resin from which anactivated carbon cannot be produced because it is melted and decomposedas a temperature is raised, if an activation treatment is carried outbefore a treatment to impart infusibility. However, when theheat-fusible resin is treated to impart infusibility, and then isactivated, an activated carbon can be produced therefrom. The“heat-fusible resin” is the term opposite to the heat-infusible resin.The heat-infusible resin means a resin from which an activated carboncan be produced by the proceeding of carbonization (accompanying somedecomposition) without melting as a temperature is raised, even if atreatment to impart infusibility is not carried out in advance. Thetreatment to impart infusibility is, for example, an oxidation treatmentcarried out at 150° C. to 400° C. under an atmosphere containing oxygen,as mentioned below.

A typical example of the heat-fusible resin is a thermoplastic resin,such as a cross-linked vinyl resin. A typical example of theheat-infusible resin is a thermosetting resin, such as a phenol or furanresin. Any known thermoplastic resin from which a spherical shape isformed can be used. In the present invention, the heat-fusible resinincludes the thermosetting resin from which an activated carbon can beobtained by the activation after the treatment to impart infusibility,but it is melted and decomposed as a temperature is raised, if anactivation treatment is carried out before a treatment to impartinfusibility. Thus, any thermosetting resin which has the above propertyand from which a spherical shape is formed can be used. When thespherical activated carbon or the surface-modified spherical activatedcarbon is produced from the cross-linked vinyl resin, the abovetreatment to impart infusibility is necessary. On the other hand, theabove treatment to impart infusibility is not necessary when thespherical activated carbon or the surface-modified spherical activatedcarbon is produced from an ion-exchange resin prepared by applyingfunctional groups to the cross-linked vinyl resin. It is believed thatthe cross-linked resin is modified from the heat-fusible resin to theheat-infusible resin by the treatment used to introduce the functionalgroups thereto, and the functional groups introduced thereby. That is,the cross-linked vinyl resin belongs to the heat-fusible resin as usedherein, whereas the ion-exchange resin belongs to the heat-infusibleresin as used herein.

The sphere of the heat-fusible resin, such as the cross-linked vinylresin, used as a starting material may be, for example, a sphericalpolymer prepared by an emulsion polymerization, a bulk polymerization,or a solution polymerization, preferably a spherical polymer prepared bya suspension polymerization. When the spherical cross-linked vinyl resinhaving a particle diameter of 50 μm or more is treated to uniformlyimpart infusibility, pores must be formed in advance in the cross-linkedvinyl resin. The pores can be formed in the resin by adding porogenduring the polymerization step. The surface area of the cross-linkedvinyl resin required to uniformly impart infusibility thereto ispreferably 10 m²/g or more, more preferably 50 m²/g or more.

For example, when the cross-linked vinyl resin is prepared by asuspension polymerization, an organic phase containing vinyl monomers, across-linking agent, porogen, and a polymerization initiator is added toan aqueous dispersion medium containing a dispersion-stabilizing agent,the whole is mixed with stirring to form many organic droplets suspendedin an aqueous phase, and the monomers in the organic droplets arepolymerized by heating, to thereby prepare the spherical cross-linkedvinyl resin.

As the vinyl-based monomer, any vinyl-based monomer from which aspherical shape can be formed may be used. For example, an aromaticvinyl-based monomer, such as styrene, a styrene derivative wherein ahydrogen atom of a vinyl group or a phenyl group is substituted, or acompound wherein a heterocyclic or polycyclic compound is bonded to avinyl group instead of a phenyl group can be used. An example of thearomatic vinyl-based monomer may be α- or β-methyl styrene, α- orβ-ethyl styrene, methoxy styrene, phenyl styrene, or chlorostyrene, or,o-, m-, or p-methyl styrene, ethyl styrene, methoxy styrene, methylsilylstyrene, hydroxylstyrene, chloro-styrene, cyanostyrene, nitrostyrene,aminostyrene, carboxy-styrene, or sulfoxystyrene, sodium styrenesulfonate, or vinyl pyridine, vinyl thiophene, vinyl pyrrolidone, vinylnaphthalene, vinyl anthracene, or vinylbiphenyl. Further, an aliphaticvinyl-based monomer can be used. For example, there may be mentionedvinyl esters such as ethylene, propylene, isobutylene, diisobutylene,vinyl chloride, acrylate, methacrylate, or vinyl acetate; vinylketonessuch as vinyl methyl ketone, or vinyl ethyl ketone; vinylaldehydes, suchas acrolein, or methacrolein; vinylethers, such as vinylmethylether, orvinylethylether; or vinyl nitriles, such as acrylonitrile, ethylacrylonitrile, diphenyl acrylonitrile, chloroacrylonitrile.

Any cross-linking agent which may be used for the cross-lining of theabove vinyl-based monomer may be used. For example, there may bementioned divinylbenzene, divinyl-pyridine, divinyltoluene,divinylnaphthalene, diallyl phthalate, ethylene glycol diacrylate,ethylene glycol dimethylate, divinylxylene, divinylethylbenzene,divinyl-sulfone, polyvinyl or polyallyl ether of glycol or glycerol,polyvinyl or polyallyl ether of pentaerythritol, polyvinyl or polyallylether of mono or dithio derivative of glycol, polyvinyl or polyallylether of resorcinol, divinyl ketone, divinyl sulfide, allyl acrylate,diallyl maleate, diallyl fumarate, diallyl succinate, diallyl carbonate,diallyl malonate, diallyl oxalate, diallyl adipate, diallyl sebacate,triallyl tricarballylate, triallyl aconitate, triallyl citrate, triallylphosphate, N,N′-methylene diacrylamide,1,2-di(α-methylmethylenesulfoneamido)ethylene, trivinylbenzene,trivinylnaphthalene, polyvinylanthracene, or trivinylcyclohexane. AParticularly preferable cross-linking agent is polyvinyl aromatichydrocarbon, such as divinylbenzene, glycol trimethacrylate such asethylene glycol dimethacrylate, or polyvinyl hydrocarbon such astrivinyl cyclohexane). Divinylbenzene is most preferable, because of anexcellent property of thermal decomposition.

As an appropriate porogen, there may be mentioned alkanol having 4 to 10carbon atoms, such as, n-butanol, sec-butanol, 2-ethylhexanol, decanol,or 4-methyl 2-pentanol, alkyl ester having at least 7 carbon atoms, suchas n.-hexyl acetate, 2-ethylhexyl acetate, methyl oleate, dibutylcebacate, dibutyl adipate, or dibutylcarbonate, alkyl ketone having 4 to10 carbon atoms, such as dibutyl ketone or methyl isobutyl ketone, oralkyl carboxylic acid, such as heptanoic acid, aromatic hydrocarbon,such as toluene, xylene, or benzene, higher saturated aliphatichydrocarbon, such as hexane, heptane, or isooctane, or cyclic aliphatichydrocarbon, such as cyclohexane.

A polymerization initiator is not particularly limited, and an initiatorusually used in this field can be used in the present invention. An oilsoluble initiator which is soluble in a polymerizable monomer ispreferable. As an example of the polymerization initiator, there may bementioned a dialkyl peroxide, a diacyl peroxide, a peroxyester, aperoxydicarbonate, or an azo compound. More particularly, a dialkylperoxide, such as methylethyl-peroxide, di-t-butyl peroxide, or dicumylperoxide; a diacyl peroxide, such as isobutylperoxide, benzoylperoxide,2,4-dichloro-benzoylperoxide, or 3,5,5-trimethylhexanoyl peroxide; aperoxyester, such as t-butylperoxypyvalate, t-hexyl-peroxypyvalate,t-butylperoxyneodecanoate, t-hexylperoxy-neodecanoate, 1-cyclohexyl1-methylethylperoxyneodecanoate,1,1,3,3-tetramethylbutylperoxyneodecanoate, cumyl peroxy-neodecanoate,or (α,α-bisneodecanoyl peroxy)diisopropyl-benzene; a peroxydicarbonate,such as bis(4-t-butyl-cyclohexyl)peroxy-dicarbonate, di n-propyl-oxydicarbonate, diisopropyl peroxydicarbonate,di(2-ethylethylperoxy)-dicarbonate, dimethoxybutylperoxy-dicarbonate,di(3-methyl 3-methoxybutylperoxy)dicarbonate; or an azo compound, suchas 2,2′-azobisisobutylonitorile,2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile,2,2′-azobis(2,4-dimethylvalero-nitrile), or1,′-azobis(1-cyclohexanecarbonitrile).

The composition of the cross-linked vinyl resin is not limited. In themanufacturing process of the present invention, however, the oxidationstep and the activation step are carried out. Therefore, thecross-linked vinyl resin preferably does not contain elements such assulfur, nitrogen, or halogen, which may possibly become a noxious gas,or an oxide of which may become a noxious gas. Further, such elementsmay remain in the spherical activated carbon, and thus, influencestherefrom are inestimable.

Therefore, a content of elements other than a carbon atom, a hydrogenatom, and an oxygen atom in the heat-fusible resin (cross-linked vinylresin) is preferably 15% by weight or less, more preferably 10% byweight or less, and particularly preferably 5% by weight or less.

According to the present process, various properties, such as an averageparticle diameter, a pore volume, a particle size distribution, or aspecific surface area, of the finally resulting spherical activatedcarbon or surface-modified spherical activated carbon can be controlledby variously changing the manufacturing conditions in the step offorming the sphere of the heat-fusible resin. For example, the averageparticle diameter and the particle size distribution of the sphericalactivated carbon or the surface-modified spherical activated carbonvaries with the size of droplet in an aqueous phase, and the size of thedroplet can be controlled by an amount of a suspending agent, the numberof stirring revolutions, a shape of the stirring blade, or a monomerratio in an aqueous phase, that is, a ratio of an amount of water and anamount of monomers. For example, the size of the droplet can be loweredby increasing an amount of a suspending agent, or increasing the numberof stirring revolutions. Further, it is preferable to decrease an amountof monomers in an aqueous phase, not only because an aggregation ofdroplets can be controlled, but also because a heat of polymerizationcan be easily removed. However, it is not preferable, in view ofproductivity, that an amount of monomer ratio is too low, because anamount of monomers per a batch, and thus, an amount of synthetic resinproduced is decreased.

When the controlled pore diameter is 10 nm or more, the pore volume andthe specific surface area can be controlled mainly by an amount and akind of porogen. When the controlled pore diameter is 10 nm or less, thepore volume and the specific surface area can be controlled byconditions of steam activation. In addition, the microtexture as thespherical activated carbon or the surface-modified spherical activatedcarbon can be controlled by a kind of a resin, a kind and an amount of across-linking agent, conditions for imparting infusibility, and/oractivating temperature, or the like.

It is preferable that the average particle diameter and the particlesize distribution of the heat-fusible resin sphere prepared in this stepare approximately equal to those of the desired spherical activatedcarbon or the surface-modified spherical activated carbon.

The second step in the manufacturing process of the present invention isto oxidize the heat-fusible resin sphere to form a heat-infusiblespherical substance.

When the heat-fusible resin sphere is directly activated, the sphere issoftened and changed to an aspherical shape, or fused together. Thus,the softening can be inhibited by an oxidation at 150° C. to 400° C. inan atmosphere containing oxygen, as a treatment to impart infusibility.If the temperature is too low, the oxidation would unfavorably beinsufficient, and if the temperature is too high, the resin wouldunfavorably be decomposed. The optimal temperature at the oxidationtreatment varies with the period of the oxidation treatment. A prolongedretention time has the effect same as that of an elevation of thetemperature of the oxidation treatment. However, the prolonged retentiontime causes the lowered industrial productivity, and thus, the shorterretention time (period of oxidation treatment) is preferable. In such asense, the temperature ultimately elevated in the oxidation treatment ispreferably 230° C. to 350° C., more preferably 250° C. to 330° C. Thedegree of infusibility can be judged from a content of oxygen in theproduct prepared by imparting infusibility to the heat-fusible resin,i.e., the heat-infusible sphere. The oxygen content is preferably 7% to25% by weight, more preferably 10% to 23% by weight, particularlypreferably 10% to 20% by weight.

Further, if many pyrolysis gases or the like are generated by theheat-treatment of the spherical heat-fusible resin which has beentreated to impart infusibility, pyrolysis products may be removed inadvance by carrying out a pre-calcination, prior to the activation. Ifthe temperature of pre-calcination is too low, pyrolysis would beinsufficient. Therefore, the temperature of pre-calcination ispreferably 500° C. to 1000° C. The pre-calcination can be carried out ina moving bed, a fluidized bed, or a fixed bed, but the fluidized bed ispreferable, because an adhesion of tar or the like to the resin or afusion of particles is lowered.

The third step in the manufacturing process of the present invention isto activate the heat-infusible spherical substance to form the sphericalactivated carbon.

In the activating treatment, procedures substantially the same as aconventional method for production from pitch can be used. For example,the heat-infusible spherical substance can be activated at 700 to 1000°C. in a gas stream reactive with carbon to obtain the sphericalactivated carbon. For example, the gas stream reactive with carbon maybe prepared by diluting the reactive gas with non-reactive gas, such asnitrogen. The activating rate varies with a composition, a concentrationor a temperature of gas used. For example, when steam is used, thereaction commences at about 700° C., but the reaction rate is very slow.When the temperature is 1000° C. or more, the reaction rate becomeshigh, and thus, a diffusion rate of the reaction gas is a ratedetermining step of the activation and the control of the activationdegree, whereby a good pore structure is not obtained. The reason thatthe diffusion rate of the reaction gas becomes a rate determining stepis that the reaction rate becomes rapid more than the rate of the gasdiffusing into the inside of the particle, and thus, the activationreaction occurs dominantly on the particle surface. Therefore, theactivating temperature is more preferably 760° C. to 1000° C.,particularly preferably 800° C. to 1000° C. The activation can becarried out in a moving bed, a fluidized bed, or a fixed bed, but thefluidized bed is preferable, because a temperature distribution in areaction system is narrow and thus, a homogeneous activation isfacilitated, a relatively large amount of the reactive gas is easilycharged into the reaction system, and the spherical material easily andthus, homogenously flows.

As mentioned above, in the desired spherical activated carbon orsurface-modified spherical activated carbon, the pore structure having apore diameter of 10 nm or less, particularly 3 nm or less can beadjusted by controlling the activation degree. Specifically, microporesare formed in an initial stage of the activation, and then, themicropores are changed to pores having a larger pore diameter, as theactivation proceeds.

The term “activated carbon” as used herein means a porous productprepared by a heat-treatment of a carbon precursor such as a sphericalheat-infusible resin, and a subsequent activation, and the term“spherical activated carbon” as used herein means an activated carbonhaving a spherical shape and a specific surface area of 100 m²/g ormore.

According to the present process comprising the above first step to thethird step, for example, a spherical activated carbon wherein an averageparticle diameter is 0.01 to 1 mm, a specific surface area determined bya BET method is 700 m²/g or more, and a volume of pores having a porediameter of 7.5 to 15000 nm is 0.01 mL/g to 1 mL/g can be prepared. Thatis, a spherical activated carbon wherein the average particle diameteris any value within the range of 0.01 to 1 mm, for example, 40 to 1000μm, 40 to 600 μm, or 50 to 200 μm, the specific surface area determinedby a BET method is any value within the range of 700 m²/g or more, forexample, 700 to 3000 m²/g, 1100 to 2500 m²/g, or 1300 to 2500 m²/g, andthe volume of pores having a pore diameter of 7.5 to 15000 nm is anyvalue within the range of 0.01 mL/g to 1 mL/g, for example, 0.01 to 0.5mL/g, 0.01 to 0.25 mL/g, or 0.01 to 0.1 mL/g, can be prepared.

In the present invention, a step of oxidizing and reducing the abovespherical activated carbon to form a surface-modified sphericalactivated carbon can be further carried out as a fourth step followingthe third step.

The spherical activated carbon is oxidized at 300 to 800° C., preferably320 to 600° C., in an atmosphere containing 0.1 to 50 vol %, preferably1 to 30 vol %, particularly preferably 3 to 20 vol % of oxygen, and thenreduced at 800 to 1200° C., preferably 800 to 1000° C., in an atmosphereof non-oxidative gas, to thereby obtain the surface-modified sphericalactivated carbon. Pure oxygen, nitrogen oxide, air, or the like can beused as an oxygen source in the particular atmosphere containing oxygen.The atmosphere inactive to carbon means nitrogen, argon, or helium,alone or a mixture thereof. The term “surface-modified sphericalactivated carbon” as used herein means a porous product prepared by theoxidizing and reducing treatments of the spherical activated carbon asabove, wherein acidic and basic sites are added in a well-balancedmanner on the surface of the spherical activated carbon to therebyimprove an adsorbability of harmful substances. For example, specificityto or selective adsorbability of harmful substances to be adsorbed canbe enhanced by the oxidizing and reducing treatments of the sphericalactivated carbon as above.

According to the present process comprising the above first step to thefourth step, for example, a surface-modified spherical activated carbonwherein an average particle diameter is 0.01 to 1 mm, a specific surfacearea determined by a BET method is 700 m²/g or more, a volume of poreshaving a pore diameter of 7.5 to 15000 nm is 0.01 mL/g to 1 mL/g, atotal amount of acidic groups is 0.30 to 1.20 meq/g, and a total amountof basic groups is 0.20 to 0.90 meq/g, can be prepared. That is, aspherical activated carbon wherein the average particle diameter is anyvalue within the range of 0.01 to 1 mm, for example, 30 to 1000 μm, 40to 600 μm, or 50 to 200 μm, the specific surface area determined by aBET method is any value within the range of 700 m²/g or more, forexample, 700 to 3000 m²/g, 1100 to 2500 m²/g, or 1300 to 2500 m²/g, andthe volume of pores having a pore diameter of 7.5 to 15000 nm is anyvalue within the range of 0.01 mL/g to 1 mL/g, for example, 0.01 to 0.5mL/g, 0.01 to 0.25 mL/g, or 0.01 to 0.1 mL/g, the total amount of acidicgroups is any value within the range of 0.30 to 1.20 meq/g, for example,0.30 to 1.00 meq/g, 0.30 to 0.80 meq/g, or 0.40 to 0.70 meq/g, and thetotal amount of basic groups is any value within the range of 0.20 to0.90 meq/g, for example, 0.30 to 0.80 meq/g, 0.40 to 0.80 meq/g, or 0.40to 0.70 meq/g, can be prepared.

Properties of the spherical activated carbon or the surface-modifiedspherical activated carbon prepared by the process of the presentinvention, namely, the average particle diameter, the specific surfacearea, the pore volume, the particle size distribution, the total amountof acidic groups, and the total amount of basic groups, are measured bythe following methods.

(1) An Average Particle Diameter (Dv50)

A particle-sizes accumulating standard curve with respect to a volumebasis is prepared by a laser diffraction apparatus for measuringparticle size distribution [SALAD-3000S; Shimadzu Corporation]. Aparticle size at a particle-sizes accumulating ratio of 50% isdetermined as an average particle diameter (Dv50).

(2) A Bulk Density

This is measured in accordance with a method for measuring a packingdensity defined in JIS K 1474-5.7.2.

(3) A Specific Surface Area (Method for Calculating a Specific SurfaceArea by a BET Method)

An amount of gas adsorbed is measured by a specific surface areameasuring apparatus (for example, ASAP2010 manufactured byMICROMERITICS) in accordance with a gas adsorbing method for thespherical activated carbon sample or the surface-modified sphericalactivated carbon sample, and a specific surface area can be calculatedby the following adsorption equation. More particularly, the sphericalactivated carbon or the surface-modified spherical activated carbon ischarged as a sample in a sample tube, and dried under a reduced pressureat 300° C. Thereafter, a weight of a dried sample is measured. Then, thetest tube is cooled to −196° C., and nitrogen is introduced into thetest tube, whereby nitrogen is adsorbed to the spherical activatedcarbon sample or the surface-modified spherical activated carbon sample.A relation of a nitrogen partial pressure and an adsorbed amount(absorption-isotherm line) is measured.

BET plotting is carried out, given that a relative pressure of nitrogenis p, and an adsorbed amount at that time is v(cm³/g STP). That is, theplotting in a range wherein p is 0.02 to 0.20 is carried out, in thefield wherein a longitudinal axis is p/(v(l-p)), and an abscissa axis isp. Given that the gradient at that time is b(g/cm³) and an intercept isc(g/cm³), a specific surface area S (unit=m²/g) can be calculated fromthe equation:

S=[MA×(6.02×10²³)]/[22414×10¹⁸×(b+c)]  [equation 1]

wherein MA denotes a cross-sectional area of a nitrogen molecule, and is0.162 nm².

(4) A Specific Surface Area (Method for Calculating a Specific SurfaceArea by a Langmuir's Equation)

An amount of gas adsorbed is measured by a specific surface areameasuring apparatus (for example, ASAP2010 manufactured byMICROMERITICS) in accordance with a gas adsorbing method for thespherical activated carbon sample or the surface-modified sphericalactivated carbon sample, and a specific surface area can be calculatedby Langmuir's adsorption equation. More particularly, the sphericalactivated carbon or the surface-modified spherical activated carbon ischarged as a sample in a sample tube, and dried under a reduced pressureat 300° C. Thereafter, a weight of a dried sample is measured. Then, thetest tube is cooled to −196° C., and nitrogen is introduced into thetest tube, whereby nitrogen is adsorbed to the spherical activatedcarbon sample or the surface-modified spherical activated carbon sample.A relation of a nitrogen partial pressure and an adsorbed amount(absorption-isotherm line) is measured.

Langmuir's plotting is carried out, given that a relative pressure ofnitrogen is p, and an adsorbed amount at that time is v(cm³/g STP). Thatis, the plotting in a range wherein p is 0.02 to 0.20 is carried out, inthe field wherein a longitudinal axis is p/v, and an abscissa axis is p.Given that the gradient at that time is b(g/cm³), a specific surfacearea S (unit=m²/g) can be calculated from the equation:

S=[MA×(6.02×10²³)]/[22414×10¹⁸ ×b]  [equation 2]

wherein MA denotes a cross-sectional area of a nitrogen molecule, and is0.162 nm².

(5) A Pore Volume by a Mercury Injection Method

The pore volume can be measured by a mercury porosimeter (for example,AUTOPORE 9200 manufactured by MICROMERITICS). The spherical activatedcarbon or the surface-modified spherical activated carbon is charged asa sample in a sample vessel, and degassed under a pressure of 2.67 Pa orless for 30 minutes. Then, mercury is introduced into the sample vessel,a pressure applied is gradually increased (maximum pressure=414 MPa) toforce the mercury into the micropores in the spherical activated carbonsample or the surface-modified spherical activated carbon sample. A porevolume distribution of the spherical activated carbon sample or thesurface-modified spherical activated carbon sample is measured from arelationship between the pressure and an amount of forced mercury, byequations as mentioned below.

Specifically, a volume of mercury inserted into the spherical activatedcarbon sample or the surface-modified spherical activated carbon samplewhile a pressure is applied is increased from a pressure (0.06 MPa)corresponding to a pore diameter of 21 μm to the maximum pressure (414MPa) corresponding to a pore diameter of 3 nm. A pore diameter can becalculated as follows. When mercury is forced into a cylindricalmicropore having a diameter (D) by applying a pressure (P), a surfacetension (γ) of mercury is balanced with a pressure acting on a sectionof the micropore, and thus, a following equation is held:

nDγ cos θ=π(D/2)² ·p

wherein θ is a contact angle of mercury and a wall of the micropore.Therefore, a following equation:

D=(−4γ cos θ)/P

is held.

In the present specification, the relationship between the pressure (P)and the pore diameter (D) is calculated by an equation:

D=1.27/P

given that a surface tension of mercury is 484 dyne/cm, a contact angleof mercury and carbon is 130°, a unit of the pressure P is MPa, and aunit of the pore diameter D is μm. The volume of pores having a porediameter of 20 to 15000 nm in the present invention corresponds to avolume of mercury inserted by applying a pressure increasing from 0.08MPa to 63.5 MPa.

(6) Particle Size Distribution

A number-based particle distribution is measured by a laser diffractionapparatus for measuring particle size distribution [SALAD-3000S;Shimadzu Corporation] and a representative particle size D and thenumber n in a fraction of particles having particle size to be measuredare determined. A length average particle diameter D₁, and a weightaverage particle diameter D₄ were calculated by the following equations:

D ₁=Σ(nD)/Σn  [equation 3]

D ₄=Σ(nD ⁴)/Σ(nD ³)  [equation 4]

(7) Total Amount of Acidic Groups

The total amount of acidic groups is an amount of NaOH consumed, whichmay be determined by adding 1 g of the spherical activated carbon sampleor the surface-modified spherical activated carbon sample, after beingcrushed to form particles having a size of 200 mesh or less, to 50 mL ofa 0.05N NaOH solution, shaking the mixture for 48 hours, then filteringout the spherical activated carbon sample or the surface-modifiedspherical activated carbon sample, and titrating until neutralization.

(8) Total Amount of Basic Groups

The total amount of basic groups is an amount of HCl consumed, which maybe determined by adding 1 g of the spherical activated carbon sample orthe surface-modified spherical activated carbon sample after beingcrushed to form particles having a size of 200 mesh or less, to 50 mL ofa 0.05N HCl solution, shaking the mixture for 24 hours, then filteringout the spherical activated carbon sample or the surface-modifiedspherical activated carbon sample, and titrating until neutralization.

The spherical activated carbon which can be prepared by the process ofthe present invention, or particularly, the surface-modified sphericalactivated carbon which can be obtained from the above sphericalactivated carbon exhibits an excellent adsorbability of exacerbationfactors of liver diseases or harmful substances of renal diseases, andtherefore, may be used as an adsorbent for an oral administration fortreating or preventing a renal disease or a liver disease.

As the renal disease, there may be mentioned, for example, chronic renalfailure, acute renal failure, chronic pyelonephritis, acutepyelonephritis, chronic nephritis, acute nephritic syndrome, acuteprogressive nephritic syndrome, chronic nephritic syndromes nephroticsyndrome, nephrosclerosis, interstitial nephritis, tubulopathy, lipoidnephrosis, diabetic nephropathy, renovascular hypertension, orhypertension syndrome, or secondary renal diseases caused by theseprimary diseases, or a light renal failure before a dialysis therapy,and may be used in an improvement of a light renal failure before adialysis therapy or a disease condition for a patient during a dialysistherapy (see “Clinical Nephrology”, Asakura-shoten, Nishio Honda,Kenkichi Koiso, and Kiyoshi Kurokawa, 1990; and “Nephrology”Igaku-shoin, Teruo Omae and Sei Fujimi, ed., 1981).

As the liver disease, there may be mentioned, for example, fulminanthepatitis, chronic hepatitis, viral hepatitis, alcoholic hepatitis,hepatic fibrosis, liver cirrhosis, hepatic cancer, autoimmune hepatitis,drug allergic hepatopathy, primary biliary cirrhosis, tremor,encephalopathia, dysbolism, or dysfunction. Further, the porousspherical carbonaceous substance can be used in a treatment of a diseasecaused by toxic substances in a body, such as psychosis.

EXAMPLES

The present invention now will be further illustrated by, but is by nomeans limited to, the following Examples.

Example 1

Deionized water (220 g) and methyl cellulose (58 g) were charged into a1 L separable flask. Further, 105 g of styrene, 184 g of divinyl benzenewith a purity of 57% (57% divinylbenzene and 43% ethylvinyl benzene),1.68 g of 2,2′-azobis(2,4-dimethylvaleronitrile), and 63 g of 1-butanolas a porogen were added thereto. Then, a replacement with a nitrogen gaswas carried out. The two-phase system was stirred at 200 rpm, and heatedto 55° C., and then allowed to stand for 20 hours. The resulting resinwas filtered, and dried in a rotary evaporator. In a vacuum dryer,1-butanol was removed from the resin by distillation, and the productwas dried under a reduced pressure at 90° C. for 12 hours to therebyobtain a spherical porous synthetic resin having an average particlediameter of 180 μm. A specific surface area of the porous syntheticresin was about 90 m²/g.

The resulting spherical porous synthetic resin (100 g) was charged intoa reactor having a grating, and treated to impart infusibility in avertical tubular furnace. The infusibility-imparting treatment wascarried out under the conditions that dried air (3 L/min) was upwardlypassed from the lower portion of the reactor tube, the temperature wasraised to 260° C. at a rate of 5° C./h, and the whole was allowed tostand at 260° C. for 4 hours to thereby obtain a spherical porousoxidized resin. The resulting spherical porous oxidized resin washeat-treated at 600° C. for 1 hour under a nitrogen atmosphere, and thenactivated in a fluidized bed at 820° C. for 10 hours under a nitrogengas atmosphere containing 64.5% by volume of steam, to obtain aspherical activated carbon. The properties of the resulting sphericalactivated carbon are shown in Table 1.

Then, the resulting spherical activated carbon was oxidized in thefluidized bed at 470° C. for 195 minutes under a nitrogen-oxygenatmosphere containing 18.5% by volume of oxygen, and reduced in thefluidized bed at 900° C. for 17 minutes under a nitrogen gas atmosphere,to obtain a surface-modified spherical activated carbon. The propertiesof the resulting surface-modified spherical activated carbon are listedin Table 2.

Example 2

The procedures of Example 1 were repeated except that the two-phasesystem was stirred at 100 rpm, instead of 200 rpm, to obtain a sphericalactivated carbon and a surface-modified spherical activated carbon. Theproperties of the resulting spherical activated carbon are listed inTable 1, and the properties of the surface-modified spherical activatedcarbon are listed in Table 2.

Example 3

The procedures of Example 1 were repeated except that the two-phasesystem was stirred at 150 rpm, instead of 200 rpm, to obtain a sphericalactivated carbon and a surface-modified spherical activated carbon. Theproperties of the resulting spherical activated carbon are listed inTable 1, and the properties of the surface-modified spherical activatedcarbon are listed in Table 2.

Example 4

The procedures of Example 1 were repeated except that the two-phasesystem was stirred at 300 rpm, instead of 200 rpm, to obtain a sphericalactivated carbon and a surface-modified spherical activated carbon. Theproperties of the resulting spherical activated carbon are listed inTable 1, and the properties of the surface-modified spherical activatedcarbon are listed in Table 2.

Example 5

The procedures of Example 1 were repeated except that the activation wascarried out for 6 hours, instead of 10 hours, to obtain a sphericalactivated carbon and a surface-modified spherical activated carbon. Theproperties of the resulting spherical activated carbon are listed inTable 1, and the properties of the surface-modified spherical activatedcarbon are listed in Table 2.

Example 6

The procedures of Example 1 were repeated except that the activation wascarried out for 13 hours, instead of 10 hours, to obtain a sphericalactivated carbon and a surface-modified spherical activated carbon. Theproperties of the resulting spherical activated carbon are listed inTable 1, and the properties of the surface-modified spherical activatedcarbon are listed in Table 2.

[Method for Evaluation of the Spherical Activated Carbon and theSurface-Modified Spherical Activated Carbon]

The properties shown in the following Table 1 (spherical activatedcarbon) and Table 2 (surface-modified spherical activated carbon) weremeasured by the following methods.

(1) Average Particle Diameter

The laser diffraction apparatus for measuring particle size distributionas mentioned above was used for the measuring.

(2) Pore Volume

The spherical activated carbon or the surface-modified sphericalactivated carbon prepared in Examples 1 to 5and Comparative Examples 1to 4 was measured by the mercury injection method as mentioned above.

(3) Specific Surface Area by BET or Langmuir's Method

The BET or Langmuir's method as mentioned above was used for themeasuring.

(4) Bulk Density

The sample was charged into a 50 mL graduated measuring cylinder untilthe sample reached a scale of 50 mL. After the cylinder was tapped 50times, a weight of the sample was divided by a volume of the sample tofind a bulk density. The results are shown in Tables 1 and 3. It wasconfirmed that the results obtained by the above method were equal tothose obtained by the method for determining a packing density inaccordance with JIS K 1474-5.7.2 in the range of the significant figuresshown in Tables 1 and 2.

(5) Total Amount of Acidic Groups and Total Amount of Basic Groups

The surface-modified spherical activated carbon sample (1 g), whichcomprised particles having a size of 200 mesh or less prepared bycrushing, was added to 50 mL of a 0.05N NaOH solution (total amount ofacidic groups) or 50 mL of a 0.05N HCl solution (total amount of basicgroups). After the mixture was shaken for 48 hours, the surface-modifiedspherical activated carbon sample was filtered out, and titrated untilneutralization to find an amount of NaOH consumed (total amount ofacidic groups) or an amount of HCl consumed (total amount of basicgroups). The results are shown in Table 2.

TABLE 1 Average Specific surface particle diameter area Length LangmuirBET Bulk Dv50 D₁ Weight D₄ method method density (μm) (μm) (μm) D₄/D₁(m²/g) (m²/g) (g/mL) Example 1 Cross-linked 117 118 133 1.12 2407 19060.50 vinyl resin Example 2 Cross-linked 198 168 196 1.16 2451 1978 0.50vinyl resin Example 3 Cross-linked 150 142 156 1.09 2380 1921 0.50 vinylresin Example 4 Cross-linked 70 67 74 1.11 2422 1955 0.50 vinyl resinExample 5 Cross-linked 119 119 135 1.14 1443 1177 0.63 vinyl resinExample 6 Cross-linked 117 128 132 1.03 2715 2210 0.47 vinyl resin

TABLE 2 Average Specific surface particle diameter area Total TotalLength Langmuir BET Bulk acidic basic Dv50 D₁ Weight D₄ method methoddensity groups groups (μm) (μm) (μm) D₄/D₁ (m²/g) (m²/g) (g/mL) (meq/g)(meq/g) Example 1 Cross-linked 111 104 129 1.24 2147 1763 0.50 0.59 0.61vinyl resin Example 2 Cross-linked 168 161 184 1.14 2206 1809 0.50 0.600.58 vinyl resin Example 3 Cross-linked 131 131 144 1.10 2142 1756 0.500.62 0.63 vinyl resin Example 4 Cross-linked 63 62 69 1.11 2180 17880.50 0.55 0.60 vinyl resin Example 5 Cross-linked 93 95 105 1.10 16141282 0.63 0.53 0.57 vinyl resin Example 6 Cross-linked 100 101 114 1.132259 1858 0.47 0.65 0.60 vinyl resin

INDUSTRIAL APPLICABILITY

According to the process of the present invention, the sphericalactivated carbon having desired properties, such as the average particlediameter, the particle size distribution, the pore volume, or thespecific surface area, can be easily obtained. Further, from the abovespherical activated carbon, the surface-modified spherical activatedcarbon having desired properties, such as the average particle diameter,the particle size distribution, the pore volume, or the specific surfacearea, can be easily obtained.

Although the present invention has been described with reference tospecific embodiments, various changes and modifications obvious to thoseskilled in the art are possible without departing from the scope of theappended claims.

1. A process for manufacturing a spherical activated carbon, comprisingthe steps of: (1) forming a spherical substance containing heat-fusibleresin, (2) oxidizing the spherical substance of the heat-fusible resinto form a heat-infusible spherical substance, and (3) activating theheat-infusible spherical substance to form the spherical activatedcarbon.
 2. The process according to claim 1, for manufacturing thespherical activated carbon wherein an average particle diameter is 0.01to 1 mm, a specific surface area determined by a BET method is 700 m²/gor more, and a volume of pores having a diameter of 7.5 to 15000 nm is0.01 mL/g to 1 mL/g.
 3. The process according to claim 1, furthercomprising the step of: oxidizing and reducing the spherical activatedcarbon to form a surface-modified spherical activated carbon.
 4. Theprocess according to claim 3, for manufacturing the surface-modifiedspherical activated carbon wherein an average particle diameter is 0.01to 1 mm, a specific surface area determined by a BET method is 700 m²/gor more, a volume of pores having a diameter of 7.5 to 15000 nm is 0.01mL/g to 1 mL/g, a total amount of acidic groups is 0.30 to 1.20 meq/g,and a total amount of basic groups is 0.20 to 0.90 meq/g.
 5. The processaccording to claim 1, wherein the heat-fusible resin is cross-linkedvinyl resin.
 6. The process according to claim 1, wherein the specificsurface area of the spherical substance of the heat-fusible resin is 10m²/g or more.
 7. The process according to claim 1, wherein the contentof elements other than carbon atom, hydrogen atom, and oxygen atom inthe heat-fusible resin is 15% by weight or less.
 8. The processaccording to claim 1, wherein the spherical activated carbon for anadsorbent for oral administration is prepared.
 9. The process accordingto claim 2, wherein the spherical activated carbon for an adsorbent fororal administration is prepared.
 10. The process according to claim 5,wherein the spherical activated carbon for an adsorbent for oraladministration is prepared.
 11. The process according to claim 6,wherein the spherical activated carbon for an adsorbent for oraladministration is prepared.
 12. The process according to claim 7,wherein the spherical activated carbon for an adsorbent for oraladministration is prepared.
 13. The process according to claim 3,wherein the heat-fusible resin is cross-linked vinyl resin.
 14. Theprocess according to claim 3, wherein the specific surface area of thespherical substance of the heat-fusible resin is 10 m²/g or more. 15.The process according to claim 3, wherein the content of elements otherthan a carbon atom, a hydrogen atom, and an oxygen atom in theheat-fusible resin is 15% by weight or less.
 16. The process accordingto claim 3, wherein the surface-modified spherical activated carbon foran adsorbent for oral administration is prepared.
 17. The processaccording to claim 4, wherein the surface-modified spherical activatedcarbon for an adsorbent for oral administration is prepared.
 18. Theprocess according to claim 9, wherein the surface-modified sphericalactivated carbon for an adsorbent for oral administration is prepared.19. The process according to claim 10, wherein the surface-modifiedspherical activated carbon for an adsorbent for oral administration isprepared.
 20. The process according to claim 11, wherein thesurface-modified spherical activated carbon for an adsorbent for oraladministration is prepared.